This disclosure relates to an apparatus for the cutting of earth formations and, more particularly, to drum-type cutters on mining machines.
Machines for cutting earth formations such as coal and other mineral deposits, rocky soil, etc., often employ rotary cutters comprising cylindrical cutter drums which carry pointed cutter bits. The cylindrical drums are connected to a rotary drive shaft that rotates the drums at the same time that the cutter is advanced against an earth formation to cut there through.
In some mining machines, for example, carrier arms extend forwardly from a vehicle body and carry a rotary cutter mechanism that rotates about a transverse horizontal axis. The cutter mechanism comprises a support housing and a drive shaft assembly rotatably mounted within the housing, and a series of longitudinally spaced cutter drums connected to the drive shaft assembly to be rotatably driven thereby.
Some of the cutter drums (outside drums) are located to the outside of the carrier arms and comprise one-piece cylinders that can be slid axially over the housing and suitably fastened in place. Others of the drums (inside drums) are located between the carrier arms. These inside drums cannot be conveniently removed in an axial direction and thus are usually formed of semi-cylindrical segments that can be separated radially to provide access to the support housing and drive shaft assemblies for maintenance. Such a mining machine is illustrated in O'dell U.S. Pat. No. 4,190,296, which includes a plurality of cutter drums connected to a drive shaft assembly, the cutter drums including a first pair of cutter drums located longitudinally outwardly of a pair of arms, and a second pair of drums located between the arms, each of the second drums comprising a pair of semi-cylindrical segments.
More particularly, the center drum two halves are bolted together during installation on the machine's cutter head shaft. There is therefore a seam, commonly called a “split line”, at the interface between the two halves. Generally, the interface between the two halves all lies within a single plane.
An array of bit holders is welded to both halves of the drum. The axial and angular position of the bit holders is carefully selected to provide desired cutting characteristics. A welding fixture is used to provide the precise locating of the bit holders.
In some cases, the desired location of a bit holder falls on the split line (seam) in the drum. When this happens, the usual solution has been to locate the bit holder as close as possible to the desired location, while avoiding the split line. This compromised bit holder location will often result in rough cutting and failure of bits, bit holders, and drive components. Another solution, rarely used, is to weld the bit holder in the preferred location, even though that means welding it across the split line. Welding across the split line is undesirable because it must be done at machine assembly time or even underground, without the benefit of the fixture for precise positioning. The overlapping bit holder also makes later drum removal difficult. Further, the welding of a bit holder on a split line may not be as robust as a fully supported holder since the mating surfaces do not fit up perfectly.
There therefore exists a need for a continuous miner center drum in which all the bit holders can be placed in the optimum locations.